1. Field of the Invention
The present invention relates to magnetic sensors, in which giant magnetoresistive elements are formed on a single substrate so as to detect intensities of magnetic fields in two-axial directions and three-axial directions. The present invention also relates to manufacturing methods of magnetic sensors.
This application claims priority on Japanese Patent Application No. 2007-156378, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, giant magnetoresistive elements (GMR elements) and tunnel magnetoresistive elements (TMR elements) have been know as elements for use in magnetic sensors. Each of these magnetoresistive elements includes a pin layer whose magnetization direction is fixed (or pinned) and a free layer whose magnetization direction varies in response to an external magnetic field, wherein it produces a resistance based on the relativity between the magnetization direction of the pin layer and the magnetization direction of the free layer. Magnetic sensors using magnetoresistive elements have been disclosed in various documents such as Patent Document 1.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-261400.
Patent Document 1 teaches a magnetic sensor in which magnetoresistive elements are formed on planar surfaces and slopes (or inclines that are inclined to planar surfaces) on a single substrate, thus detecting intensities of magnetic fields in two-axial directions and three-axial directions.
In order to improve ferromagnetism resistance of pin layers, magnetic sensors have been recently developed using giant magnetoresistive elements having synthetic antiferromagnetic (SAF) structures, in which Ru layers (where Ru stands for ruthenium) are incorporated in magnetic layers of pin layers.
The aforementioned giant magnetoresistive elements form multiple band-shaped giant magnetoresistive films (referred to as GMR bars), in which specific materials for use in pin layers and free layers are exposed on the periphery thereof. For this reason, in order to secure water resistance, heat resistance, and electric insulation, protection films (or passivation films) including oxide films and nitride films are formed by way of plasma chemical vapor deposition (i.e. plasma CVD).
In the formation of oxide films for protecting giant magnetoresistive elements by way of plasma CVD, giant magnetoresistive elements may absorb active oxygen existing in chambers. When giant magnetoresistive elements absorb oxygen, they may be locally oxidized. This drawback also occurs in the formation of protection films for coating tunnel magnetoresistive elements by way of plasma CVD.
When materials for use in free layers of GMR bars including giant magnetoresistive elements are oxidized, free layers are degraded in weak magnetic characteristics; this makes it difficult to precisely produce resistances based on magnetization directions of free layers. This also increases hysteresis loops of magnetism, thus degrading hysteresis characteristics of magnetic sensors. This drawback occurs with respect to giant magnetoresistive elements formed on planar surfaces and slopes; in particular, it remarkably occurs with respect to giant magnetoresistive elements formed on slopes.
GMR bars are formed using giant magnetoresistive elements by way of ion milling, wherein, within exposed peripheral portions of GMR bars, their side portions lying along longitudinal directions are inclined (or semi-tapered) to substrates. Within GMR bars composed of giant magnetoresistive elements formed on slopes, upward GMR bars (formed on upward slopes) and downward GMR bars (formed on downward slopes) differ from each other in inclinations (or inclined shapes). Compared with upward GMR bars, downward GMR bars are reduced in inclination; that is, downward GMR bars are reduced in thickness so that exposed areas thereof increase; hence, they are easily affected by oxidization.